140 INFECTION AND RESISTANCE 



complete dissolution of 2 milligrams of culture material 14 (of a 

 standard culture) and saving the life of the animal. The unit of 

 the serum in the preceding test would accordingly be 0.005 c. c., and 

 the titre of the serum, expressed in Pfeiffer's language, would be 

 200 units to the cubic centimeter. Owing to the great variation in 

 the virulence and toxicity of different strains of the same organism, 

 and also because of the difficulties opposed to the visible dissolution 

 of many bacteria, which may be killed by the serum without show- 

 ing much evidence of solution, the practical application of Pfeiffer's 

 standardization is not universally possible. In doing experiments 

 by this technique, whatever their purpose may be, accurate adjust- 

 ment of bacterial amounts and preliminary studies of virulence must 

 be made in order that the tests may be of real value and, failing 

 visible lysis, the death of the animals must be taken as the indicator 

 of the titration. Comparisons of results obtained with two different 

 cultures of the same species are consequently of value only when the 

 minimal lethal dose of each and its toxicity have been studied before 

 the final tests are made. 



The cardinal points of Pfeiffer's phenomenon were rapidly con- 

 firmed, but his assumption that the process could take place only 

 within the animal body was soon corrected by both Metchnikoff 15 v 

 and Bordet. 16 Both of these investigators succeeded in producing 

 extracellular lysis of cholera spirilla in hang-drop preparations. The 

 former produced the phenomenon by adding to the hang-drop prep- 

 arations small quantities of extracts of leukocytes, and thus at- 

 tempted to correlate Pfeiffer's observations with his own opinions 

 regarding the importance of the leukocytes in bacterial destruction. 

 The latter, however, subjected the phenomenon of bacteriolysis, both 

 in vivo and in vitro, to a careful analysis and obtained results which 

 definitely disproved the necessity of cellular intervention in this 

 phenomenon, and furnished facts regarding the process which stand 

 uncontradicted to the present day. Upon the basis of these our 

 modern views of the mechanism of cytolysis in general are founded. 



Bordet showed that the bacteriolytic properties of immune serum 

 are indeed destroyed by heating to from 50 to 60 C. If, however, 

 to such a heated immune serum there is added a small quantity of 

 fresh normal serum, the bacteriolytic power is restored with undi- 

 minished vigor. He recognized in consequence that there were two 

 distinct serum elements necessary for the process. Fresh normal 

 serum by itself had very slight or no bacteriolytic power. Fresh 

 immune serum had powerful and rapid effects. Heated immune 



14 The standard "loop" used in many laboratories for the rough meas- 

 urement of quantities of bacteria from agar cultures takes up approximately 

 2 milligrams of the material. 



15 Metchnikoff. Ann. de Vlnst. Past., Vol. 9, 1895. 



16 Bordet. Ann. de Vlnst. Past., Vol. 13, 1899. 



