OCTOBEE 25, 1912] 



SCIENCE 



565 



rounded by a fine proteid membrane. This 

 membrane is impermeable to lecithin. 



During the exchange of water for chloro- 

 form a characteristic structure appears in the 

 droplet. It is at first clear but within 30 sec- 

 onds becomes filled with a dense mass of gran- 

 ules (probably water) so that it looks white 

 against a dark background. The droplet is 

 still mostly chloroform, as may be determined 

 by pricking it with a needle. The contents do 

 not mix with the water. 



In the course of an hour, the dense granular 

 structure disappears and the drop clears. 

 There remain only a few dense granules (prob- 

 ably some form of lecithin) mostly aggregated 

 together to form an excentric knot like a 

 karyosome. It is in this stage, which is stable 

 and persists until destroyed by bacteria, that 

 the resemblances to sea urchin eggs are most 

 marked. 



If pricked with a needle the contents flow 

 slowly out as a viscid protoplasm-like mass 

 and mix (except the granules) with the water. 

 No chloroform is now present. 



The cells are not rigidly spherical in shape, 

 as oil globules suspended in water, but present 

 exactly those slight irregularities which may 

 be observed in freshly laid sea urchin eggs. 



The surface film is similar to the surface 

 membrane of a sea urchin egg in appearance 

 and also in consistency, as indicated by its 

 resistance to pricking and to pressure. 



Weutral red is accumulated from dilute solu- 

 tion by the cell as a whole but in particular 

 by the granules, which stain very deeply. 



Such red stained cells are tiirned yellow at 

 the same rate by w/2,000 NaOH and n/2,000 

 NH^OH. In regard to their permeability re- 

 lations they therefore diiier markedly from 

 marine eggs, which are entered much more 

 rapidly by ISTH^OH. They possess also no 

 polarity except one attributable to gravity. 



These artificial lecithin cells resemble egg 

 cells in one more important and striking re- 

 spect. If a trace of saponin is added to the 

 sea water in which sea urchin eggs lie, the 

 eggs almost instantly swell and the contents 

 become more fluid and clear, i. e., the eggs 

 cytolyze. Exactly the same thing happens 



when a trace of saponin is added to water con- 

 taining lecithin cells. They sweU and become 

 clear spheres with only a few granules in the 

 interior. The similarity is indeed perfect. 



Future work may indicate methods by which 

 protein can be obtained within a lecithin 

 membrane, the whole of a size comparable with 

 cell size, or can be introduced into lecithin 

 cells. Such cells promise to exhibit even more 

 striking and interesting properties than those 

 herein described. 



E. Newton Haevey 



Woods Hole, Mass., 

 September 6, 1912 



A METHOD OF DETERMINING THE AVERAGE LENGTH 

 OF LIFE OF FARM EQUIPMENT 



In determining the cost of farm operations 

 one of the most diifieult items to determine 

 accurately is the rate of depreciation of farm 

 equipment. Eecently Mr. H. H. Mowry, of 

 the Office of Farm Management, who has col- 

 lected extensive data on the problem of de- 

 preciation of farm equipment, suggested to 

 the writer the possibility of determining the 

 average length of life of a farm implement 

 from data relating to the number of years 

 each implement has been used. Apparently a 

 solution for this problem has been found. 

 The solution applies to all objects, either ani- 

 mate or inanimate, lasting for varying lengths 

 of time. 



Two cases are to be considered, namely, 

 (1) when the number of the objects under 

 consideration is approximately constant from 

 year to year, and (2) when their number is 

 increasing or decreasing. The first case may 

 be conveniently considered in its application 

 to farm dwellings. Suppose that on a given 

 group of farms there is a definite number of 

 farm dwellings of various ages, and that as 

 fast as old dwellings become unsuited to their 

 purpose they are replaced by new ones. For 

 convenience of reference let us reduce the 

 numbers with which we have to deal to sym- 

 bols. Let iVj represent the number of dwell- 

 ings in their first year of life, N^ the number 

 in their second year, N^ the number in their 

 third year, and so on, iV„ representing the 



