PROTOPLASM AND COLLOIDS 



191 



any transformation readily detectable by 

 simple microscopic observation. Fortu- 

 nately, however, the centrifuge is a great 

 help; and by determinations of protoplas- 

 mic viscosity one can have a trustworthy 

 indication of what is hajjpening within 

 living cells. 



In some ways protoplasm behaves like 

 an ordinary protein. The usual protein co- 

 agulants, such as alcohol, salts of heavy 

 metals, etc., have a rapid effect on the fluid 

 protoplasm and soon change it into a stiff 

 mass. But protoplasm differs from an 



Fig. 2. The effect of alkalinization on sea-urchin 

 egg protoplasm. A shows normal centrifuged cells. 

 The lower 2 cells are not properly oriented to show 

 the layers of the protoplasm, but the upper 2 cells 

 clearly show the free fat at the pole of the egg 

 opposite the heavily pigmented region. B and C 

 show cells centrifuged after alkalinization; the 

 amount of free fat is much greater than in the 

 control. 



ordinary protein solution in being far more 

 sensitive. In addition to the ordinary pro- 

 tein coagulants, various physical and chem- 

 ical agents, some of which have but little if 

 any effects on proteins, produce violent 

 change within the protoplasm. In the short 

 space of this lectnre it is scarcely pos- 

 sible to review adequately information al- 

 ready obtained concerning the effect of 

 many different agents on protoplasm. One 

 fact stands out. Various diverse types of 

 treatment cause protoplasmic gelation ; and 

 this gelation, if carried to extremes, is asso- 

 ciated with a characteristic change in the 

 appearance of the protoplasm. Instead of 

 containing onh^ granules, the cell becomes 

 filled Avith tiny vacuoles until it may look 

 like a foam. The observation that vacuoles 

 may appear in protoplasm is hardlj' new. 

 The earliest and most famous pioneer in 

 protoplasmic study, Diijardin, emphasized 



the importance of vacuolization. Indeed, in 

 some of his writing he stated that the 

 ability to form vacuoles was the outstand- 

 ing characteristic of living substance, the 

 very characteristic which most clearly dis- 

 tinguished it from inanimate proteins. 

 Through the years many authors have noted 

 protoplasmic vacuolization following ex- 

 posure of cells to hypotonic solutions, to 

 hypertonic solutions, to heat, to cold, to 

 radiation of various sorts, to the electric 

 current, and indeed following exposure to 

 almost any type of stimulating agent. 

 However, since Diijardin, very little at- 

 tempt has been made to gather together 

 or to coordinate these observations. In 

 sea-urchin eggs vacuole formation is readily 

 observed. When the cell becomes filled 

 with vacuoles it is, of course, dead; but it 

 is an important fact that all those agents 

 which excite the cell to activity cause 

 vacuolization when used in excess. 



How shall we interpret the vacuolization 

 process? One way to understand it is to 

 consider another general reaction of proto- 

 plasm, a reaction known long before the 

 discovery of the cell theory and yet until 

 recently rarely studied. Whenever a cell is 

 so torn or broken that its contents flow out, 

 a new film tends to be formed about the 

 exuding droplet. This reaction, which I 

 have called the surface precipitation reac- 

 tion, may produce only a film at the surface, 

 or it may extend more and more deeply into 

 the body of the protoplasm. If it extends 

 into the mass of the protoplasm, instead of 

 a single film, it produces countless vacuoles. 

 Both film formation and vacuolization de- 

 pend on the presence of calcium. In the 

 absence of calcium ion there is no film and 

 no vacuolization. If, then, we are to under- 

 stand vacuolization, we must understand 

 the surface precipitation reaction. 



In many ways the reaction which occurs 

 when a cell is torn or broken is comparable 

 to blood clotting. If we add oxalate salts 

 to blood as it pours from a vessel, the 

 oxalate precipitates out calcium and clot- 

 ting is prevented. So, too, with the living 

 cell. If we break a cell in the presence of 

 an oxalate solution, the contents of the pro- 



