INTRODUCTORY XV 
the pure mucous, also contains a united gland of serous and mucous secretion. 
The venom-glands of the serpents belong to the mixed structure. This 
relation gradually passes to the opposite direction and finally all find in the 
parotid of the mammalia a pure serous gland. 
The proportion of the mucous and serous parts of the venom-glands is 
quite variable, according to the kind of snake, but the serous portion, which 
occupies the rear of the gland, is much larger than the mucous-secreting 
front portion. The only secretory duct is provided for the serous or venom- 
secreting portion, while the front portion has several smaller ducts. 
That the venomous serpents differ from the non-venomous kinds only by 
the presence of a specific poison-conducting fang in the upper jaw, but not 
by the presence or absence of the venom-gland, has been shown by Leydig, 
Duvernoy, Stannius, and others. 
Phisalix, Bertrand, Jourdain, Alcock, Rogers, and others found that the 
innocuous serpents possess venom-glands of a primitive stage of evolution. 
Having briefly defined the position among the physiological secretions, its 
polytropism, its biological place in zoological sense, its probable chemical 
composition, and the phylogenic views and facts on the venomous snakes in 
the system of nature, I propose to define snake venom in relation to immunity. 
Since the monumental discovery of diphtheria antitoxin by Behring and 
Kitasato and of tetanus antitoxin by Kitasato in 1890, the solution of the 
problems of immunity has been laid open to experimental investigations. 
With fluctuating success and failure, pharmacologically active and inactive 
biological products of almost every kind have been tried for the possible 
production of specific antibody. There have resulted Pfeiffer’s bacterio- 
lysin, Carbone-Belfanti’s hemolytic serum, Ehrlich’s antiricin and antiabrin 
serums, and many other preparations of specific nature. Numerous attempts, 
some futile and some successful, have led to the conclusion that all alkaloids 
and similar simple substances of definite chemical constitution are not capable 
of producing their antibodies when injected into the animal bodies. Agglu- 
tinins, precipitins, and various antiferments have also been produced by 
means of injecting cells, proteins, or ferments, each highly specific to the 
antigen concerned. 
It was found that bacterial toxins, various somatic cells and their constitu- 
ents, phytotoxins, blood cells and ferments are responded to by the forma- 
tion of their corresponding antisubstances, and that in each instance the 
interaction is specific. 
Calmette, Phisalix and Bertrand, and somewhat later Fraser, have shown 
that the blood serum of the animal repeatedly inoculated with snake venom 
counteracts the action of the venom very effectively. This was done in 
1894, and extended by various investigators. Sewall was, however, the first 
(in 1887) to show that the repeated inoculations of a snake venom into sus- 
ceptible animals render the latter more resistant to the action of the same 
poison. 
