ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 259 



He deals first with artificial parthenogenesis. J. Loeb's experiments 

 upon the ova of Eehinoderms showed that it was possible by the use of 

 saline solutions of various strengths to initiate 'developmental changes. 

 The most successful and suggestive chemical excitant was a dilute cyanide 

 solution, in which DO p.c. of unfertilised ova developed into larvae. 



Roux, Herbst, and others have directed their attention to the medium 

 in which development takes place, and to the importance of its con- 

 stituents. By altering the quantities of oxygen, water, and salts in this 

 medium, development was variously influenced. 



Injury to the ovum in its earliest stages, deprivation of chromatin, 

 shaking apart of blastomeres, amputation of blastomeres, artificial fusion 

 of ova, and the effects of such mechanical interferences, form the subject 

 of the next series of researches here reviewed. Others have studied the 

 abnormalities of development caused by interference at a later stage 

 with the primitive layers and organ-rudiments by mechanical and other 

 means. 



In the remainder of the paper the recent work upon regeneration, 

 transplantation, and functional correlation are reviewed. Full references 

 are given throughout, rendering the article a valuable guide to the subject. 



Simple Method of Counting Leucocytes.* — This method, devised by 

 V. T. Carruthers, depends upon the fact that when equal-sized drops of 

 diluted blood are placed on a clean slide, they should cover equal areas 

 and contain equal numbers of cells. Drops of blood, well diluted, are 

 placed on a grease-free slide by means of a grease-free glass rod, and 

 allowed to dry. The blood-pigment is washed off with water and the 

 slide is stained with watery methylene-blue. A number of fields in each 

 film are counted. By means of an obturator inserted in the eye-piece of 

 the Microscope, the author has simplified the enumeration process. By 

 comparing a few counts with the numbers obtained with a Thoma-Zeiss 

 ha?matocytometer, a standard is obtained, so that from the average number 

 of leucocytes in a field, the degree of leucocytosis can be calculated. For 

 all counts, the degree of dilution must, of course, be the same, and the 

 same glass rod and obturator must be used. The successful application 

 of this method depends upon careful observation of a number of trivial 

 details, for an account of which the original paper should be consulted. 



Method of Estimating the Hardness of Minerals.! — B. Halle 

 claims that this method of estimating hardness by grinding, devised by 

 him, is superior to the scratching methods. By the latter method it is 

 difficult to get constant results owing to variations in the quality of the 

 diamond point used, and to the difficulty of maintaining even pressure 

 during the scratching process. In Halle's method the mineral is 

 ground on a revolving brass plate for a definite time, and the loss of 

 weight is observed. The specific weight of the mineral is known. All 

 the other factors — time, pace and pressure of grinding, grinding material 

 — are constant, and therefore the only variable, proportional loss of 

 weight, gives the relative hardness. By this method very fine differ- 

 ences in degree of hardness can be estimated. 



■ / &* 



* Brit. Med. Journ., (1909) ii. p. 1749. 



t Zeitsehr. wiss. Mikrosk., xxvi. (1909) pp. 424.-5. 



