136 PRINCIPLES OF GENERAL PHYSIOLOGY 



When cells are killed by various means, their semi-permeability is, as a rule, 

 converted into complete permeability. But there are some agents which, when 

 dilute, have not this effect, although they kill the cell. Formaldehyde in 4 per cent, 

 solution destroys the semi-permeability, but in 0*2 per cent, solution, this property 

 is preserved in an apparently normal state for a considerable time ; so that, for 

 example, Stewart (1901) was able to show that blood corpuscles, treated with 

 dilute formaldehyde, retain their normal permeability for ammonium chloride and 

 their normal impermeability for sodium chloride. Moreover, saponin and water 

 cause the same change in permeability to ions that they do in living blood, 

 although no laking takes place. It follows from these facts that the action of 

 saponin or of water does not depend on liberation of haemoglobin, but must be 

 exerted on the cell membrane. When the corpuscles, after fixation by formaldehyde, 

 are extracted with ether, which presumably removes the lipoids, the conductivity 

 of the corpuscles is increased and saponin has no further effect in this direction. 

 The inference seems to be that lipoid substances are an integral part of the mem- 

 brane and that the action of saponin is on these substances, although the possi- 

 bility is not to be forgotten that ether may produce other alterations in the nature 

 of the membrane, apart from abstraction of lipoids. 



A remarkable effect on blood corpuscles produced by cobra venom has been described by 

 Noguchi (1905). Like snake poisons in general, this is haemolytic in low concentrations, but 

 different species of animals vary much in their sensitiveness to this effect. In great e\ 

 cobra venom is not hsemolytic ; on the contrary, it prevents the hsemolytic action of saponin. 

 Even water, several times renewed, has no action on corpuscles subjected to the action of 

 large quantities of cobra venom. It seems impossible to explain this fact except on the 

 hypothesis that the membrane has become actually impermeable to water, as if converted into 

 wax or india-rubber. When washed with sodium chloride, their normal behaviour to water is 

 restored. It seems that some constituent of the membrane enters into combination with the 

 poison, forming a substance which is insoluble in water, but decomposed by sodium chloride. 



Ether and chloroform, like formaldehyde, have a different action in dilute and 

 in concentrated solutions. In the latter, they increase permeability, in the 

 former, they decrease it. Osterhout (1913) has shown this in the case of 

 Laminaria by conductivity measurements. It is to be noted, however, that the 

 decreased permeability is the reversible one and not associated with permanent 

 injury to the cells, so that it seems to be the normal narcotic effect. Further 

 facts will be found under the head of narcosis below. 



A point to be remembered is that it is not to be assumed that, when a cell is 

 killed, the semi-permeability of its membrane is necessaiily lost. It may be fixed 

 in some way. 



A cell, dying naturally, may become surrounded by a tough impenetrable 

 membrane. Penard (1890) made the following interesting observation. An 

 Amoeba, while living, had taken in the egg of a small worm. After the death 

 of the Amoeba, the egg hatched, but the worm was unable to escape through the 

 surrounding membrane. 



Heat, applied gradually, destroys the semi-permeability of the membrane. 

 EVen at 40 the pigment escapes from the red beet. A sudden rise of temperature 

 to 100 appears to be a useful fixing method for certain histological purposes, but 

 what its effect on the membrane may be, I am unable to state. 



THE NATURE OF THE MEMBRANE 



What conclusions may we, justifiably, draw from the various experimental 

 data of the preceding pages? 



In the first place, it seems certain that the membrane consists of substances 

 in the colloidal state. The marked effect of electrolytes shows this, especially the 

 fact that valency plays an important part. 



The following observations of Szucs (1910) on the diminution of the permeability of 

 Spirogyra to methyl violet are of interest. In order to produce a particular depth of staining 

 in eight minutes, the concentrations required were of potassium nitrate, 0'08 molar ; of 

 calcium nitrate, - 04 molar ; of aluminium nitrate, O'OOOo molar. It will bo seen that the 

 effect is in relation to the valency of the cation, which probably acts in a coagulating manner 



