274 



THE FORMS OF CELLS 



[CH. 



permitting the passage of certain dissolved substances (or their 

 "ions") and including or excluding others; and thus rendering 

 manifest and measurable the existence of a definite "osmotic 

 pressure." Li the case of the sperm-cells of Inachus, certain 

 quantitative experiments have been performed*. The sperm-cell 

 exhibits its characteristic conformation while lying in the serous 

 fluid of the animal's body, in ordinary sea-water, or in a 5 per 

 cent, solution of potassium nitrate ; these three fluids being all 

 "isotonic" with one another. As we alter the concentration of 

 potassium nitrate, the cell assumes certain definite forms corre- 

 sponding to definite concentrations of the salt; and, as a further 

 and final proof that the phenomenon is entirely physical, it is 

 found that other salts produce an identical effect when their 

 concentration is proportionate to their molecular weight, and 



KNO 



Pig. 95. Sperm-cells of Inachus, as they appear in saline solutions of 

 varying density. (After Koltzoff.) 



whatever identical effect is produced by various salts in their 

 respective concentrations, a similarly identical effect is produced 

 when these concentrations are doubled or otherwise proportionately 

 changed f. 



Thus the following table shews the percentage concentrations 

 of certain salts necessary to bring the cell into the forms a and c 

 of Fig. 95 ; in each case the quantities are proportional to the 

 molecular weights, and in each case twice the quantity is necessary 

 to produce the effect of Fig. 95 c compared with that which gives 

 rise to the all but spherical form of Fig. 95 a. 



* Koltzoff, N. K. , Studien iiber die Gestalt der Zelle, Arch. f. mihrosk. Anaf. 

 Lxvn, pp. 364-571, 1905; Biol. Centralbl. xxm, pp. 680-696, 1903, xxvi, 

 pp. 854-863, 1906; Arch. f. Zellforschung, ii, pp. 1-65, 1908, vii, pp. 344-423, 

 1911; Anat. Anzeiger, xli, pp. 183-206, 1912. 



t Cf. supra, p. 129. 



