140 Proceedings of the Royal Physical Society. 
settled, and throws an important light upon the whole 
question, although it cannot be regarded as necessarily 
applicable in all cases, or as the expression of a general law. 
The method is as follows:—If a mixture of venin and 
antivenin be heated to a given temperature the mixture 
loses its innocuousness. The antivenin is altered while the 
venin is not, so that the mixture is rendered lethal. This 
goes to show that the venin remains intact alongside the 
antivenin, or that it had formed a very unstable union with 
it. This method of settling this important question in other 
instances is not applicable, because in them heat affects 
equally the toxin and its antidotal serum. From this it 
appears that it cannot be assumed that the antitoxin acts by 
producing any very definite chemical change in the toxin, 
and yet, at the same time, its antidotal action is difficult to 
imagine without supposing that some such effect 1s produced. 
The next point bearing upon our general subject to which 
I would draw your attention, and which has important 
relations to questions connected with blood-serum, is certain 
functions which the white blood-corpuscles or leucocytes 
have been shown to possess. Until quite recently the white 
corpuscles of the blood received little attention, and it is 
doubtful whether they were accredited with any important 
role apart from their being a possible source of red 
corpuscles. In consequence of this ignorance, the glands 
in which they were produced had not the place given to 
them to which they are entitled, in view of the recent light 
thrown on the function of the cells produced by them. 
The new light thrown upon these cells is the outcome of 
investigations in connection with bacteriology. 
It was found that when microbes were locally inoculated, 
the results which followed indicated that an effort was 
‘exerted by nature to combat and to counteract their 
harmful influence. The specially novel discovery in this 
‘connection was the action which the hitherto almost 
despised leucocyte played in this process. It was shown, 
for instance, that what was practically an active struggle 
took place between the leucocyte and the invading microbe. 
Under certain circumstances the leucocyte was victorious, in 
