274 ANIMAL AGGREGATIONS 



Drzewina and Bohn, in their studies upon the effects of dilution 

 of sperm upon their physiology, record (1923) another interesting 

 phenomenon. As we have seen before, dilution of sperm in sea-water 

 hastens their loss of activity, and the greater the interval after dilu- 

 tion the greater is the loss of activity. Likewise, the greater the 

 dilution the more rapid is the loss of activity. Drzewina and Bohn 

 found that sperm immediately after dilution (1/5,000-1/100,000) 

 are very active, but are reduced in vitality so that, while fertihza- 

 tion is effected, abnormal development and cytolysis result. If an 

 interval is allowed between dilution and fertilization, normal de- 

 velopment is obtained. It is believed that the sperm, when diluted, 

 undergo a disturbance of equilibrium, exhibiting a "differential sen- 

 sibihty." There is httle, if any, change in fertilizing power, but a 

 considerable change in cytolyzing power. These phenomena are 

 exhibited only within certain limits of dilution and vary with the 

 season and locality. 



Treatment of sperm of sea urchins. Echinus microtuherculatus or 

 Strongylocentrotus lividus, with KCl or distilled water shortens the 

 duration of fertilizing power in proportion to duration of treatment 

 and concentration of the sperm, and also in proportion to the light in- 

 tensity; the weaker the dilution the more rapid the loss. One or 2 

 drops of normal KCl in distilled water, mixed with i cc. of sea-water 

 is a rapidly lethal dose for Infusoria, Planaria, etc. Sperm diluted to 

 i/ioo survive for 24 hours, but dilutions of 1/1,000 and 1/5,000 

 succumb much more rapidly. Certain of these relations are illus- 

 trated in Table XXXI 



Further, Drzewina and Bohn observed that in KCl, in fresh water, 

 and in the controls, within certain limits of duration of treatment 

 and of dosage of injurious substance, the nature of the liquid has 

 httle effect, but that the concentration of the sperm is the decisive 

 factor in duration of fertihzing power. A given concentration in 

 any of the foregoing media will, after a certain time, give about the 

 same percentage of fertilization. This condition is compared to a 

 colloidal suspension in that the nature of the solvent does not make 

 as much difference as the number of particles per unit volume. 



They pointed out that the spermatozoa behave as if a substance 



