124 



ANIMAL AGGREGATIONS 



of division in small volumes is approximately proportional to the 

 ratio of total surface to the volume of medium. Animals from young 

 cultures are more sensitive to limited volumes than are those from 

 old cultures. A fully bacterized medium retards the poisonous effect 

 of small volumes by furnishing more food and by tending to keep 

 the Paramecia out of the most toxic region next the glass, and by 

 binding the toxins present, thereby rendering them relatively harm- 

 less. These toxins may be of two sorts: there are the poisons which 

 may leach out of the glass into the limited amount of medium in 



sufficient quantity to have decided effects, and there are the meta- 

 bohc products of the Protozoa themselves. The question of the fixing 

 of toxins takes us somewhat afield from our present considerations 

 and will be left to be taken up later in detail. 



Unhke Crampton, Kalmus found that divisions of protozoans are 

 possible even when they are contained in small capillary tubes. Ap- 

 parently he did not subject his animals to the action of the centri- 

 fuge, which may partly account for the difference in results. How- 

 ever, when there are so many different factors operating, such as 

 composition of glass, age of culture, and bacterial flora, one cannot 

 be sure of the precise factor or factors causing the differences in 

 observed results. From his observations, Kalmus challenges the en- 

 tire conception that a small amount of available space, acting direct- 

 ly, may limit the rate of cell division and thereby the size of meta- 

 zoans. In this he overlooks the important results obtained by 



