Goiniagious mid EpizooUc Diseases. 71 



Limitation of Protection ly Sterilized Products. 

 While it is evident that there is a large field as yet uncul- 

 tivated in which the fruits of this method may be gathered, 

 yet there are obvious limitations to its application, some of 

 which may be shortly stated. 



1st. A certain number of animal plagues will recur in 

 the same system at frequent intervals. Thus aphthous 

 fever not unfrequently attacks the same herd twice in the 

 course of a single year, and the same apparently holds 

 with some forms of equine influenza. It would be foUy, 

 therefore, to expect any permanent protection from inocu- 

 lating the chemical products of these diseases. 



2d. A certain number of infectious diseases cannot be 

 said to have any limit set to their duration. Thus tuber- 

 culosis and glanders may go on for a life-time, the inflamed 

 and embryonic tissue produced under the influence of the 

 poisonous products of the germ furnishing continual acces- 

 sions of new food for the slowly developing germ, and thus 

 determining a constant extension of the colonies of bacilli. 

 It is absurd, therefore, to expect protection by the use of 

 the chemical products in these cases. 



3d. It may turn out that the ptomaines of given dis- 

 eases are volatile and would be dissipated by heat, so that 

 the final sterilized product will be deficient in the essential 

 element in which its- preventive virtue resides. In the 

 inorganic kingdom we have the alkali ammonia volatile at 

 oi-dinary temperatures, and it would not be surprising if in 

 the organic kingdom a certain number of alkaloids should 

 also prove volatile. In such cases the product sterilized by 

 heat would be useless. 



4th. It is not at all improbable that chemical or physical 

 changes may be effected by heat in the ferment or alkaloid 

 produced by a disease-germ, as egg albumen is coagulated. 

 Here again the method would be at fault. 



5th. In other methods of sterilization similar difficulties 



