RELATION TO ENVIRONMENT 145 



stances which have a chemotaxic influence on the spermatozoa; 

 and this would explain the phenomenon of fertilization which 

 would be difficult on any other basis. 



The white blood corpuscles are susceptible to chemotaxic 

 influences, and certain metamorphoses are due to this. The 

 change from the tadpole stage to the frog stage is brought 

 about because of the chemotaxic influence which certain tissues, 

 undergoing degeneration, have on the white blood corpuscles. 

 The same explanation is used for changes which take place 

 in old age, the degeneration of certain tissues, the loss of 

 pigment in hair, etc. The phenomenon of inflammation is 

 explained on this basis. The invading microorganism ex- 

 erts a chemotaxic influence on the white blood cells, which 

 cause them to leave the blood vessels and to collect around 

 the invaders, and this phenomenon is really the basis of Metch- 

 nikoffs theory of immunity, which is so widely accepted at 

 the present time. 



The phenomenon of chemotaxis can be studied under the 

 microscope by a method which was devised by Pfeiffer, and 

 which is carried out as follows : 



Selected capillary glass tubes are placed in watch glasses 

 containing the solution to be tested; they are then placed 

 under a vacuum pump and the air is drawn out so as to com- 

 pletely .fill the tubes with the solution. The tubes are then 

 thoroughly rinsed, and the open end of the filled tube is 

 plunged into a hanging drop of the bacteria to be studied. 

 The solution gradually diffuses out, and the bacteria, which 



