200 BIOLOGY OF THE PROTOZOA 



proteins are taken into the protoplasmic bodies of many kinds of 

 Protozoa by absorption through the general cortex or through some 

 specialized region for the purpose. 



From experiments with the green alga, Euglena gracilis, by Zum- 

 stein (1900), Ternetz (1912), et al., it appears probable that some 

 saprozoic forms of Protozoa get their main nourishment from 

 amino-acids derived from disintegration of animal and plant matter 

 through the agency of bacteria, and from carbohydrates in solution. 

 The necessary mineral matters are obtained from the surrounding 

 alkaline medium. 



Emery (1928), experimenting with Paramecium caudatum, found 

 that a measurable quantity of amino-acids is utilized in place of 

 the normal bacterial food. With a mixture of equal parts of ten 

 amino-acids he figured out that 100,000 Paramecium caudatum in 

 twelve hours would use 48.3 per cent of a 0.1 per cent solution, 

 while different amino-acids used singly gave differing results. 1 



In this connection, it is important to consider the possible inter- 

 action of excretion products of different Protozoa upon themselves 

 and upon each other, as well as the effects of products of bacterial 

 action. It has long been known that isolation cultures are fre- 

 quently threatened by the growth of detrimental bacteria. On 

 a 'priori grounds it is not improbable that excretion products of 

 Protozoa themselves may have such an effect. Woodruff (1912, 

 1913) has studied this problem in connection with Paramecium 

 aurelia and the hypotrichous ciliates, Stylonychia pustulata and 

 Pleurotricha lanceolata, and found that Paramecium, when placed 

 in filtered medium which had contained enormous numbers of 

 Paramecium in pure culture, were manifestly weakened in vitality. 

 Similarly the hypotrichs, when placed in filtered medium which had 

 swarmed with hypotrichs, showed a weakened vitality. When, 

 however, Paramecium was placed in filtered hypotrich culture 

 medium, the result was an increased vitality. Woodruff concluded 

 that excretion products from Paramecium are detrimental to 

 Paramecium, and hypotrich products to hypotrichs, while the 

 latter products have a somewhat stimulating effect on Paramecium. 

 This may be, as Woodruff suggests, of some importance in deter- 

 mining the sequence of protozoon forms in a limited environment 

 such as hay infusion. 



1 The degree of absorption of specific amino-acids is as follows: 



Per Per 



cent. cent. 



Mixture of different amino-acids Alanine 15.5 



(except arginine) . 48 . 3 Glutamic acid 13.2 



Glutamic acid hydrochloride . 45 . 6 Leucine 12.0 



Cysteine hydrochloride 26.3 Glycocoll 9.6 



Aspartic acid 25 . 1 Tryptophane 9.6 



Tyrosin .17.7 Phenylalanine 7.7 



Arginine 15.9 



