Protoplasmic Streatiiing — Relation to Gel Structure 129 



of the second group are considerably augmented or accelerated in 

 the lower range of pressure. Furthermore, it may be said that the 

 effect of pressure upon the activities of the first group is in propor- 

 tion to the effect upon the gel system, whereas this does not seem 

 to be the case for the second group. 



II. METHOD 



A. DIFFERENCES BETWEEN HYDROSTATIC AND OTHER TYPES OF 



COMPRESSION 



It is important to realize that the pressure used in the experi- 

 ments is of the hydrostatic type. Each cell or tissue is completely 

 surrounded by a liquid medium, and this medium serves to trans- 

 mit the pressure from the pump equally in all directions. This 

 condition eliminates all distortional injury, such as would result 

 if the tissues were compressed locally between impinging solid 

 surfaces. The difference is well illustrated by experiments on divid- 

 ing Arbacia eggs. When these cells are compressed between a slide 

 and coverslip, less than 5 Ibs./in.- suffices to cause considerable 

 distortion and to block the cleavage. Under hydrostatic compression, 

 however, the form of the egg remains unchanged, aside from a very 

 slight loss of volume, at pressures well above 10,000 Ibs./in.-, and the 

 capacity to furrow is not completely abolished until a pressure of 

 more than 5,000 Ibs./in.- is reached. 



Another important experimental condition is the absence of any 

 gas phase in the system. Many of the early experiments in the field 

 were complicated by the fact that the pressure was applied through 

 the medium of a supernatant atmosphere. This made it difficult to 

 distinguish between the effects of the pressure per se, and the effects 

 of driving excessive quantities of the atmospheric gases into solution 

 in the protoplasm and the surrounding liquid medium. When the 

 gaseous phase is eliminated, the main effect of the pressure must be 

 mediated through small changes in the protoplasmic volume" and 

 through the consequent alterations in the fundamental molecular 

 pattern of the protoplasmic system. 



B. RECENT TECHNICAL DEVELOPMENTS 



All of the experimental methods cannot be given in detail, but a 

 brief consideration of two recently developed pieces of apparatus 

 will permit a clearer understanding of the ensuing work. The first 

 is the centrifuge-pressure bomb devised by Brown ('34c). This 



