44 Proceedings of Royal Society of Edinburgh. [sess. 
in opposition to other observers, that the bacilli of the vaccines are 
smaller, this corresponding to the degree of attenuation they have 
undergone. On comparing the bacilli of Pasteur’s vaccines with the 
virulent forms when grown on gelatine and bouillon, only a very 
slight difference in their size was usually to be detected; when, how- 
ever, they originated from a potato culture, the difference became very 
marked, the 1st vaccine being only about one-half as broad as the 
virulent organism. This appears to be mainly due to the acid re- 
action of the medium affecting the vaccines more than the virulent 
organism, the size of the bacillus apparently varying with the more or 
less favourable conditions to which it is for the moment exposed. 
Huber * has observed that anthrax bacilli vary in size as they occur 
in the tissues of different species of animals, being much larger in 
the more sensitive than in the less susceptible animals. This differ- 
ence in size of the organism in different animals, or even in different 
tissues of the same animal, should not be regarded as indicating 
a more or less favourable medium in a physical sense, but rather as 
the vital expression on the part of the microbe of the influences to 
w'hich it has been there exposed, resulting from the reactive powers 
of the tissues in that special animal or even tissue. This point will 
be dealt wdth more fully presently, since it is important as evidencing 
an action exerted by the cells on the microbe which lies outside 
them. 
There is still a relation of the enzyme function to the organism 
which has not yet been discussed — the action, or rather want of 
action, which the ferments manifest on the living protoplasm. The 
organisms are constantly bathed in their own enzymes, and may even 
be exposed to those of other microbes without their substance being 
attacked by these. The explanation of Pavy,f of why self- 
digestion of the stomach does not occur in the living animal, even 
if it were sufficient in that special case, would not apply to those 
ferments which act in alkaline reaction. The “ living principle ” of 
John Hunter, J as inhibiting the action of the enzymes, seems still 
the only plausible explanation which applies to all cases. This 
question has assumed importance from a bacteriological point of 
* Deutsche med. Wochenschrift, 1881. 
t Philosoph. Transactions, page 161, 1863. 
+ Philosoph. Transactions , June 18, 1772. 
