222 



SCIENCE. 



[N. S. V(,L. XVI. No. 397. 



phoid fever, and requires, moreover, the addi- 

 tion of alum. It is the alum, not the filtra- 

 tion, which is actively concerned in the re- 

 moval of the bacteria. If enough alum is 

 added the effluent is clear and gives satisfac- 

 tory results on bacteriological examination. 

 If an insufficient quantity is added the effluent 

 may be turbid and charged with bacteria. If 

 too much is added or more than can be decom- 

 posed by the carbonates present, alum will 

 remain in solution in the effluent as a most 

 undesirable accidental constituent ; and finally, 

 the life of an English sand filter is practically 

 unlimited, while that of the mechanical type is 

 as yet undetermined. In view of all these facts, 

 the writer finds no difficulty in unhesitatingly 

 declaring in favor of the natural method of sand 

 filtration, especially as the superiority of this 

 method in the suppression of typhoid fever 

 may be accepted as acknowledged even by the 

 advocates of the mechanical process. 



Professor Sedgwick's chapter on ice as a 

 vehicle of infectious disease, the ice supply 

 and the public health, on p. 251, is especially 

 interesting; the more important facts are 

 summarized as follows : " (1) While it is true 

 that some individual bacteria survive exposure 

 to freezing and even very low temperatures, 

 such conditions are highly unfavorable to bac- 

 teria in general, even of the same kind, es- 

 pecially if the exposure be prolonged. Water 

 does certainly tend to purify itself, and under 

 ordinary and favorable circumstances does 

 actually and extensively purify itself during 

 freezing. On the other hand, such purifica- 

 tion, while great, is usually incomplete. (2) 

 Out of a number of individual bacteria of 

 any kind subjected to freezing, a large propor- 

 tion usually perish, especially if they continue 

 to be exposed to the low temperature for two 

 or three weeks, but a small proportion survive. 

 (3) There is good reason to believe that the 

 efficiency of the survivors and their virulence 

 are weakened both by their loss of numbers 

 and by freezing or by long exposure to low 

 temperatures. These facts taken together 

 with those already mentioned above enable us 

 to explain all or nearly all the phenomena in 

 question. They also enable us to draw im- 

 portant conclusions concerning the dangers 



of the pollution of ice and concerning ice sup- 

 ply and the public health." 



In the next paragraph he says : " Although 

 from what has now been said it is clear that 

 there is much truth in the popular opinion 

 that water purifies itself in freezing; it is 

 equally plain that too much reliance must not 

 be placed upon this process. Ice should be 

 made only from good raw materials, i. e., from 

 waters which are pure and potable, and this 

 is doubly true if 'artificial' rather than 'nat- 

 ural' ice is to be used for public or private 

 supplies." In view of these difficulties the 

 writer has urged upon his students for years 

 the dangers of mingling of melted or cracked 

 ice with food and drink, for apart from the 

 possibility of infected ice he is convinced 

 that many of the digestive derangements so 

 common in this country are induced by the 

 low temperatures of food and drink. A tem- 

 perature of between 50° and 60° F. is suffi- 

 cientl,y low to be refreshing, and for this pur- 

 pose he recommends that the bottles contain- 

 ing the filtered or boiled water and other 

 articles of food be set on ice or placed in a 

 cold storage." 



Chapter XL, on milk as a vehicle of infec- 

 tious disease, is also extremely valuable and 

 must be read to be thoroughly appreciated. 

 Ihe importance of this article of food in rela- 

 tion to public health has been thoroughly 

 studied; the present writer continued the 

 investigations made by Mr. Ernest Hart in 

 1881 and presented his coricluBions, based 

 upon the tabulated histories of 330 outbreaks 

 of infectious diseases spread through the milk 

 supply, before the International Medical Con- 

 gress at Paris in 1900; these outbreaks consist 

 of 195 epidemics of typhoid fever, 99 epi- 

 demics of scarlet fever and 36 epidemics of 

 diphtheria. On page 284 the author says : 

 " One of the most startling discoveries re- 

 cently made 'in regard to infectious materials 

 in milk is that of Dr. Stokes and an asso- 

 ciate, of Baltimore, who investigated a curi- 

 ous creamy yellowish layer of a slightly sus- 

 picious appearance upon milk derived from a 

 dairy tributary to that city. They found that 

 the yellow layer was largely composed of pus 

 and finally traced its origin to a herd affected 



