INTRODUCTION 43 



strated by a number of typical forms of living Protozoa, this struc- 

 ture is difficult to make out in other types. Thus in the endoplasm 

 of flagellates like Chilomonas, or the endoplasm of Actinophrys sol, 

 or Actinosphaerium eichhornii, the alveoli are easily discernible, but 

 in Paramecium caudatum, in many gregarines, and in many types 

 of flagellates and ciliates, the alveoli, if present, are too fine to be 

 seen with the usual powers of the microscope. Vonwiller (1918) 

 can find no evidence for upholding the alveolar theory of proto- 

 plasmic structure in general. 



Certainly in many cases the protoplasm appears to be almost 

 homogeneous in structure, the granules alone being evidence of 

 structural configuration. Such forms are illustrations of the gran- 

 ula theory of Altmann, who held that protoplasm is made up of a 

 congeries of such granules or microsomes each of which is termed a 

 bioblast, each bioblast being regarded as a single unit performing 

 all of the functions of living matter including growth and reproduc- 

 tion. Here, however, theoretical considerations have been super- 

 imposed on the obvious structure and the physical appearances 

 become clouded in a mist of speculation. Other theories, such as 

 the reticular and fibrillar theories, associated with the names of 

 Heitzmann, Schafer, Flemming, etc., are based upon the actual 

 pictures of different types of protoplasm. 



The larger vacuoles in different types of Protozoa to which the 

 names cavulae, gastric, and contractile vacuoles are given are inter- 

 preted according to the alveolar theory as due to the flowing together 

 and fusion of adjacent alveoli. This is certainly the case in the for- 

 mation of a contractile vacuole of Amoeba proteus where the begin- 

 nings of a vacuole may be watched under the microscope and the 

 coalescence of minute vesicles noted. In a similar way the relatively 

 huge cavulae or pseudo-alveolae characteristic of Actinosphaerium 

 eichhornii and of Radiolaria may be accounted for. 



Physically, protoplasm is to be compared with an emulsion of 

 colloidal substances which, as Lord Rayleigh and others have 

 pointed out, as a polyphasic system can retain the emulsoid condi- 

 tion only as long as the limiting membranes between dispersed and 

 dispersing media are intact. In the activities of a living, moving 

 cell, there must be a continual disturbance of this physical equi- 

 librium and a constantly changing configuration of the protoplasm 

 due to the manifold chemical actions which are characteristic of 

 living matter. 



Chemically, protoplasm is not a substance but a harmoniously 

 working aggregate of different interacting substances which have 

 been identified in general as nucleins, nucleo-albumins, nucleo-pro- 

 teins, lipoproteins, fats, carbohydrates, salts and the almost endless 

 variety of derivatives from these and from their combinations. 

 But the chemical make up of living substance is, as yet, in an 



