36 POPULAR SCIENCE MONTHLY. 



with more or less success in reference to other diseases like plague and 

 typhoid fever. The study of immunity has also rendered possible what 

 may be called curative inoculation, or the injection of antitoxic ma- 

 terial as a cure for diphtheria, tetanus, snake poisoning, etc. 



The power the blood possesses of slaying bacteria was first discovered 

 when the effort was made to grow various kinds of bacteria in it; it 

 was looked upon as probable that blood would prove a suitable soil or 

 medium for this purpose. It was found in some instances to have ex- 

 actly the opposite effect. The chemical characters of the substances 

 which kill the bacteria are not fully known; indeed, the same is true 

 for most of the substances we have to speak of in this connection. 

 Absence of knowledge on this particular point has not, however, pre- 

 vented important discoveries from being made. 



So far as is known at present, the substances in question are proteid 

 in nature. The bactericidal powers of blood are destroyed by heating 

 it for an hour to 56 C. Whether the substances are enzymes is a 

 disputed point. So also is the question whether they are derived from 

 the leucocytes; the balance of evidence appears to me to be in favor of 

 this view in many cases at any rate, and phagocytosis becomes more in- 

 telligible if this view is accepted. The substances, whatever be their 

 source or their chemical nature, are sometimes called alexins, but the 

 more usual name now applied to them is that of bacterio-lysins. 



Closely allied to the bactericidal power of blood, or blood-serum, 

 is its globulicidal power. By this one means that the blood-serum of one 

 animal has the power of dissolving the red blood-corpuscles of 

 another species. If the serum of one animal is injected into the 

 blood-stream of an animal of another species, the result is a destruction 

 of its red corpuscles, which may be so excessive as to lead to the passing 

 of the liberated hemoglobin into the urine (hemoglobinuria). The 

 substance or substances in the serum that possess this property are 

 called hemolysins, and though there is some doubt whether bacterio- 

 lysins and hsemo-lysins are absolutely identical, there is no doubt that 

 they are closely related substances. 



Another interesting chemical point in this connection is the fact 

 that the bactericidal power of the blood is closely related to its 

 alkalinity. Increase of alkalinity means increase of bactericidal 

 power. Venous blood contains more diffusible alkali than arterial blood 

 and is more bactericidal; dropsical effusions are more alkaline than 

 normal lymph and kill bacteria more easily. In a condition like 

 diabetes, when the blood is less alkaline than it should be, the suscepti- 

 bility to infectious diseases is increased. Alkalinity is probably bene- 

 ficial because it favors those oxidative processes in the cells of the body 

 which are so essential for the maintenance of healthy life. 



