Much effort was underway in nineteenth century London to improve the health of the public.  Besides contaminated water, the air was polluted with heavy fumes from various industries.  The prevailing miasma theory focused attention on the sanitary state of the environment, presenting a sound instinct but incomplete biological understanding of the link between exposure factors and disease.

To address some of these disease-transmission problems, a law  was passed by Parliament in 1846 (Nuisances Removal and Diseases Prevention Act).  It was commonly known as the Cholera Bill, and likely was favored by Dr. John Snow.  The bill was used during the cholera epidemic of 1848-9 to encourage property owners to clean their dwellings and connect them to sewers. 

Proposed Admendment

Several years later in 1855, an amendment to the Act was proposed to regulate industries such as gas works, bone-boiling works and similar establishments which released fumes into the atmosphere.  Supporters of the miasma theory favored this amendment, feeling that causative agents of disease are transmitted by air, killing with effluvia, and thus should be addressed by the manufacturers.  Being a strong supporter of the germ theory (perhaps too strong, extending his thoughts to diseases other than cholera which may have a respiratory origin), Dr. Snow was asked by various manufacturers to testify on the proposed amendment. This he did as the second witness on March 5, 1855 to a Parliamentary committee chaired by Sir Benjamin Hall (1802-67, see figure). 

Hall was a legislator who in 1855 became Chief Commissioner of Works and was responsible for improvements to the royal parks and for the final stage of the rebuilding of the Houses of Parliament.  He was a tall, imposing man and was the source of the name "big Ben" for the new clock in the Parliament (see figure). Although not a physician, Hall became a strong proponent of environmental sanitation and public health, perhaps due to his belief in the miasma theory and the need for cleanliness of vapors. 

The Testimony

John Snow was called to testify regarding his beliefs. The questions on March 5, 1855 are in maroon and Snow's response in black.  Thus the testimony was based on Snow's notions and opinions, but was not supported with experimentation or other research studies, or illustrated with tables or graphs.  

117. [Chairman, Sir Benjamin Hall] “Do you practice as a medical man in the Metropolis?”

”Yes, in Sackville Street.”

118. “You wish to give some evidence upon the Nuisances Removal and Diseases Prevention Act?”

”I have been requested to give evidence on behalf of the trades people in the south districts of London, more particularly.”

119. “Upon what point?”

”I received a request from Mr. Knight. I was asked if I would give evidence on behalf of the manufacturers whose interests are threatened by the Nuisances Removal Act. I have not seen the parties, nor learnt any particulars. From my printed publication they have learnt that my opinion is, that measures necessary to protect the public health would not interfere with useful trades; and I believe it is on that account that they have asked me to give evidence on their behalf, and I have expressed my willingness to do so.”

120. “To what points would you desire to draw the attention of the Committee as regards the sanitary question?”

”I have paid a great deal of attention to epidemic diseases, more particularly to cholera, and in fact to the public health in general; and I have arrived at the conclusion with regard to what are called offensive trades, that many of them really do not assist in the propagation of epidemic diseases, and that in fact they are not injurious to the public health. I consider that if they were injurious to the public health they would be extremely so to the workmen engaged in those trades, and as far as I have been able to learn, that is not the case; and from the law of the diffusion of gases, it follows, that if they are not injurious to those actually upon the spot, where the trades are carried on, it is impossible they should be to persons further removed from the spot.”

121. “Are the Committee to understand, taking the case of
bone-boilers, that no matter how offensive to the sense of smell the effluvia that comes from bone-boiling establishments may be, yet you consider that it is not prejudicial in any way to the health of the inhabitants of the district?”

"That is my opinion.”

122. [Mr Greene] “Does that extend to all animal substances?”

”No. I believe that epidemic diseases are propagated by special animal poisons coming from diseased persons, and causing the same diseases to others, and that they are extremely injurious; but that substances belonging to animals, that is to say, ordinary decomposing animal matter, will not produce disease in the human subject.”

123. “Do you apply that, also, to decaying vegetable matter; do you consider that that will not be productive of disease?”

”I do not believe that decaying vegetable matter would be productive of disease; at least, it is a matter open for discussion whether certain decomposing vegetable substances, in marshy districts, may not produce agues; but in London, in any trade I am acquainted with, I do not believe that any decomposing vegetable or animal matters produce disease.”

124. [Chairman, Sir Benjamin Hall] “Take the case of a bone-boiling establishment, or a knacker’s yard; assuming that there is a large number of horses in a state of decomposition, from which of course there would be very offensive effluvia, as far as the sense of smell is concerned, do you apprehend that that would not be prejudicial to the health of the inhabitants round?”

”I believe not.”

125. [Mr Adderley] “Have you never known the blood poisoned by inhaling putrid matter?”

”No; but by dissection wounds the blood may be poisoned.”

126. “Never by inhaling putrid matter?”

”No; gases produced by decomposition, when very concentrated, will produce sudden death; but where the person is not killed, if the person recovers, he has no fever or illness.”

127. [Mr Egerton] “You mean to say, that the fact of breathing alr which is tainted by decomposing matter, either animal or vegetable, will not be highly prejudicial to health?”

”I am not aware that it is, unless it be in such quantities as to produce actually fatal effects at the moment; but to produce those effects it requires that it should be highly concentrated.”

128. “Do you not know that the effect of breathing such tainted air often is to produce violent sickness at the time?”

”Yes, when the gases are in a very large quantity, as in a cesspool.”

129. “Do you mean to tell the Committee that when the effect is to produce violent sickness there is no injury produced to the constitution or health of the individual?“

“No fever or special disease.”

130. [Mr Greene] “Are you not aware that persons going into vaults where there are a number of dead bodies have suffered very severely, and that sometimes death has been produced by this cause?”

”Yes, when those gases are extremely concentrated, they will actually poison a person and cause death, but not cause disease; those poisons do not reproduce themselves in the constitution.”

131. “Are you not aware that, in cases of this kind, illness has sometimes been produced from which persons have suffered for a considerable length of time before death

”I am not satisfied upon that point. If illness has followed I think it has been a coincident.”

132. “Are you not aware that, in cases of this kind, illness has sometimes been produced from which persons have suffered very severely, and that sometimes death has been produced by this cause?”

”Yes, when those gases are extremely concentrated, they will actually poison a person and cause death, but not cause disease; those poisons do not reproduce themselves in the constitution.”

133. [Mr Egerton] “You say that the effluvia arising from living subjects are dangerous?”

”Or even from certain persons who have died from disease.” [These points were then repeated by Snow in response to similar questions by Mr. Wilkinson.]

138. [Chairman, Sir Benjamin Hall] “I understand you to say that such effluvia, when highly concentrated, may produce vomiting, but that they are not injurious to health. How do you reconcile those two propositions?”

”If the vomiting were repeatedly produced, it would certainly be injurious to health. If a person was constantly exposed to decomposing matter, so concentrated as to disturb the digestive organs, it must be admitted that that would be injurious to health; but I am not aware that, in following any useful trade or manufacture, the effects ever experienced.”

139. “You consider that occasional sickness would be of no consequence, but that only frequent occurrence of the attacks would be injurious?”

”I am not aware that any occasional sickness is produced in any useful trade or manufacture.”

140. [Mr Egerton] “Do you not know that the effect of a very strong offensive smell often is to produce vomiting?”

”The gases must be very concentrated to do that, except it be by a kind of sympathy. Persons are often much influenced by the imagination.”

141. “Where does your practice lie?”

”I am living in Sackville Street, Piccadilly.”

142. [Mr Wilkinson] “I believe you are frequently in the habit of administering chloroform?”


143. “And therefore your attention has been particularly called to the effect of the administration of gases ?“


144. “Have you turned your attention to the effects of the late outbreak of cholera in London?”

”Yes, I made special enquiries throughout Lambeth and Southwark and Newington.

145. “Have you satisfied yourself by those inquiries of any particular results of that outbreak of cholera, so as to state your opinion of what has been the mode of propagation of the disease?”

”I have satisfied myself completely, that the chief mode of propagation of cholera in the South district of London, throughout the late outbreak, was by the water of the Southwark and Vauxhall Water Company containing the sewage of London; and containing consequently whatever might come from the cholera patients in the crowded habitations of the poor; and I am satisfied that it spread directly from individual to individual, sometimes in the same family, but by similar means; that is, by their swallowing accidentally what came from a previous sick patient.”

146. “Do you believe that there is evidence to show that cholera has been propagated almost entirely by the poison being taken in at the mouth?”


147. “Absolutely swallowed?”

”Yes, it is my belief in every case.”

148. [Mr Egerton] “Has your practice lain much amongst the poor?”

”Not so much latterly as it did at one time; but it did very much till seven years ago.”

149. “In what district?”

”In a district near Soho Square, running as far as Seven Dials.”

150. “You have stated that in the course of your inquiry you satisfied yourself that water was the principal cause of communicating cholera, after the water had been impregnated by the existence of the cholera. Did you satisfy yourself what was the original cause of cholera in those persons who were not so affected by the water?”

”I consider that the last outbreak of cholera was introduced from the Baltic Fleet into the Thames. I consider that the cause of cholera is always cholera; that each case always depends upon a previous one.

151. “You have stated that, in your opinion, these offensive trades have no injurious effect upon the health; will you state by what means you have arrived at that conclusion; whether it is by lengthened experience derived from medical attendance upon those who carry on these trades or whether it is a theory?”

”It is derived in various ways, but chiefly rather in a negative way; from my having satisfied myself on other causes of disease quite independent of those trades; also from my general medical opinions, and also from my experience amongst trades people who have been exposed to those things.”

152. “As your medical practice has not been amongst men
who follow those occupations, by what means do you arrive at the fact that their health is not affected by them?”

”I have attended people in every occupation, and my opinion is derived also from reading, and from personal information.”

153. “Is your opinion derived from practical experience, or is it mere theory of your own?”

”My theory is derived from practice, and from observation.”

154. “Will you state in what particular localities of London you practiced as a medical man, so as to be able to express that opinion so confidently to the Committee?”

”My practice amongst the poor extended chiefly between the Thames and Oxford Street; I have not turned my special attention to any particular trades; I never was called upon, till two or three days ago to consider this subject particularly.”

155. “The point at which we particularly wish to arrive here
is the effect of particular trades upon the health of individuals. You say that you believe that these offensive trades have no effect upon the health of individuals; by what means do you arrive at that conclusion?”

"Partly by my own observation, partly by reading.”

156. “Will you state where your observation was obtained; because, in the locality that you mention, between the Thames and Oxford Street, there are few, if any, soap-boilers or bone-crushers, or any of those trades?”

”There are people who collect the bones in the rag shops; but in the hospitals I have seen patients from every part of London.”

157. “Has your attention ever been directed, as a medical man, to those particular parts of London about Bermondsey, and other districts, on the south side of the water: Have you ever practiced as a medical man there?”

”I have not practiced there; I have visited patients there: but for several weeks in the last autumn I went to the houses of 700 people who had died of cholera, and I knew their actual occupations, and their age, as it was entered in the Registrar General’s reports, and I examined the tables at the time.”

158. “In what part of London did you make those inquiries?”

”Throughout the whole of Lambeth, St. George’s, Southwark, and the whole of Newington, and St. George’s Camberwell; I inquired respecting every case of cholera in the first seven weeks of the epidemic.”

159. “But you do not practice as a medical man in these particular districts?”

”No, I live in Sackville Street; I have lived there for three years; previously to that I lived in Frith Street, Soho Square. I did not attend those patients on the south side of London, but I went afterwards to the houses making inquiries, to find out the nature of their supply of water; and in doing that I learnt a number of other particulars about them. I always knew the occupation of the deceased person.”

160. [Mr. Egerton] “Do you dispute the fact that putrid fever and typhus fever hang about places where there are
open sewers?”


161. “How do you account for that?”

”It is a coincidence. Where there are open sewers you have mostly a number of people living together under such circumstances that they get fever, which is communicated from one person to another; very often the water of the pump wells is impregnated with the excrements of the people, which soaks into the wells. And the general water supply in certain districts is also very bad.”

162. [Mr. Wilkinson] “Did not you make particular inquiries
at the houses which were supplied by two companies which take their supply of water from different places?”

”Yes; the one is supplied from Battersea Fields, near Vauxhall Bridge, and the other from Thames Ditton.”

163. “Was there a very marked difference between them?”

”There was. In the first four weeks of the epidemic the mortality was fourteen times as great amongst the customers of the Southwark and Vauxhall Company, getting their water in Battersea Fields as in the other, taking into account the number of houses supplied by each company.”

164. “You have made very extensive statistical inquiry as to the diseases which you have mentioned?”

”I have.”

165. “Have you in any case traced the propagation of those diseases, or of the cholera, to the existence of offensive trades?”

”I have every reason to believe that those trades have not had any influence whatever.” 

166. “In any single instance that you have visited in those places, were you ever able to trace any case of the propagation of disease by any of the offensive trades?”

”No; on the contrary, I am satisfied that such influences have no effect whatever. Last autumn there was not much cholera about Fore Street, Lambeth, and all that district. That district suffered extremely in 1849; but in 1854 it suffered very slightly. All the other facts remain the same; but that district is now chiefly supplied by the Lambeth Company with improved water.”

[Questions were then posed concerning the cause of diseases among persons at the Milbank Prison. Of note was question 172.]

172. [Mr. Langton] “Is it not possible that the same poisonous qualities which affect the water may be floating in the air?”

”That is possible; but I believe that the poison of the cholera is either swallowed in water, or got directly from some other person in the family, or in the room; I believe it
is quite an exception for it to be conveyed in the air; though if the matter gets dry it may be wafted a short distance.”

For the reaction of The Lancet to Snow's testimony and the final disposition of the Act, click here.  

For Snow's 1856 Lancet article On the Supposed Influence of Offensive Trades on Mortality click here


Lillienfeld D. American J Epidemiology 152(1), 4-9, 2000.

Lucken B. Pollution and Control -- A Social History of the Thames in the Nineteenth Century, 1986. 

Halliday S. The Great Stink of London, 1999.

Roebuck J. Urban Development in 19th Century London -- Lambeth, Battersea & Wandsworth 1838-1888, 1979.

Wohl AS. Endangered Lives -- Public Health in Victorian Britain, 1983.


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