May 3, 1901.] 
‘resistance of tissues,’ but, as I have 
already pointed out, a chemical theory, 
implying a reaction between antivenene and 
venom, which results in a neutralization of 
the toxic activities of the venom, is entirely 
compatible with the observed facts. 
Another significant fact of chemical im- 
portance observed by Fraser is that, in car- 
rying out the immunizing process, ‘‘ the 
saturation point of the blood for antivenene 
is reached before the pessible maximum 
non-fatal dose of venom has been adminis- 
tered.”’ The protective value of venom 
and ‘antivenene’ when administered by 
the stomach has already been mentioned. 
By this time the use of diphtheria anti- 
toxin as a therapeutic agent in the treat- 
ment of diphtheria had become firmly es- 
tablished. The variation in the results 
obtained caused Ehrlich to search for a 
quantitative relation between the toxin of 
diphtheria and the antitoxin of diphtheritic 
serum. The result of Ehrlich’s investiga- 
tion is to be found in the Croonian lecture 
delivered by him before the Royal Society, 
London, March 22, 1900. ‘ By means of 
test-tube experiments with suspended ani- 
mal tissues’ he brought out some very inter- 
esting facts. ‘‘ The relations were simplest 
in the case of red-blood corpuscles. On 
them, outside the body, the action of many 
blood poisons, and of their antitoxins, can 
be most accurately studied, e. g., the actions 
of ricin, eel-serum, snake poison, tetanus 
toxine, etc. * * * By means of these test- 
tube experiments, particularly in the case 
of ricin, I was able, in the first place, to 
determine that they yielded an exact quan- 
titative representation of the course of the 
processes in the living body. * * * It was 
shown that the action of toxine and anti- 
toxine took place quantitatively as in the 
animal body. * * * It was proved in the 
ease of certain toxines—notably tetanus 
toxine—that the action of antitoxines is 
accentuated or diminished under the influ- 
SCIENCE. 
695 
ence of the same factors which bring about 
similar modifications in chemical processes 
— warmth accelerates, cold retards the re- 
action, and this proceeds more rapidly in 
concentrated than in dilute solutions. * * * 
The knowledge thus gained led easily to the 
inference that to render toxine innocuous 
by means of antitoxine was a purely chem- 
ical process, in which biological processes 
had no share.” 
The distribution of the toxins and the 
antitoxins in the system is a matter of 
prime importance, yet not more than a be- 
ginning has been imade looking toward 
their localization. That they do possess a 
selective action has been established by 
Stokvis, Donitz, Pfeiffer, Marx, Wasser- 
mann and Roux, and these facts thréw a 
great deal of light upon the phenomena of 
incubation, time reactions, antitoxic action, 
protective action, serum therapy, etc. 
The phenomena of agglutination and 
lysogenic action, the recent work of Buchner 
in Germany and Bordet in France, on 
hemolysis, and some experimental work 
on ionic reactions done in my own labora- 
tory, deserve consideration here; but time 
presses for a summation, and they must be 
passed without further comment to a future 
occasion. 
From accumulated facts, acquired immunity 
is separable into two distinct types. (The 
following classification is borrowed from 
Muir and Ritchie. ) 
A. Active immunity, 7. ¢., produced in an animal 
by an injection, or by a series of injections, of 
non-lethal doses of an organism or its toxines. 
1. By injection of the living organisms. 
(a) Attenuated in various ways. Examples: 
(1) By growing in the presence of oxygen, or 
in a current of air. 
(2) By passing through the tissues of one 
species of animal (becomes attenuated for 
another species). 
(3) By growing at abnormal temperatures, etc, 
(4) By growing in the presence of weak anti- 
septics, or by injecting the latter along with 
the organism, ete. 
