HARD WICKE' S SCIENCE- G OS SIP. 



parts by weight of whey, 6 of skim milk, I of bruised 

 barley, and i of bruised rice, are of approximately 

 equal feeding value. 



Mixed Diet v. Vegetable-food for Pigs. — 

 Another German experimenter selected six pigs from 

 the same litter lOO days old ; and three were fed on 

 I part by weight of dried blood, 6 of bran, and 14 of 

 skim milk ; the other three received an unlimited 

 amount of maize-meal. The difference of composition 

 of these two kinds of food was considerable ; in the 

 first, one half of the dry weight was albuminoid or 

 nitrogenous ; in the second, only \ or \, the excess in 

 the latter being carbo-hydrates or farinaceous food. 

 At the end of 130 days, the pigs were killed and 

 compared, with the following results. 



The total live weight of the first set was 19 per 

 cent, greater than that of the second. In 

 set I, 38 per cent, of the whole body, ex- 

 cluding bone, was fat ; in set 2 it amounted 

 to 46 per cent. The dead carcasses of 

 set I were 21 per cent- heavier than set 2 ; 

 the kidneys of set i were 42 per cent. ; the 

 spleens 33, the livers 32, the blood 59, the 

 hair and skins 36, the large muscles of the 

 back 64, the two muscles of the body 

 cavity 38, and the bones 23 per cent, 

 greater than in the second set. The 

 strength of the thigh-bones, determined by 

 a specially-contrived machine, was found to be 62 per 

 cent, greater in the first than in the second set. 



From this it is inferred by the author that by 

 varying the feeding, fat or lean can be cultivated at 

 pleasure, the carbo-hydrates being the most effective 

 fat producers, but that excessive fat is produced at 

 the expense of the muscles and to the detriment of the 

 animals if used for breeding. 



Referring again to our Christmas shows of fat 

 beasts, it would be well if some such analyses as the 

 above were made occasionally. 



As pigs in their natural state obtain neither the 

 dietary of set i nor set 2, a third set of experiments 

 might be made in which green vegetables and roots 

 should be added to the excessively farinaceous diet of 

 the third set, the absence of vegetable juices in which 

 is a serious defect. 



LAELAPS ARVOLICA. 

 Parasite of Water Rat {Arvicola amphibins). 



THIS Gamasid, so far as I know, has never been 

 described, or figured. The Gamasi are so 

 numerous that we may be thankful wherever there 

 is any well-marked structural difference enabling 

 us to form a subdivision. We have to thank Koch for 

 the division Laelaps. He describes and figures 

 four species. These were all found on mice ; two 

 of them (Z. hiUiris and Z. pachypiis) on Lcduhis 



arvalis, and two (Z. agilis and L. festimis) on Mas 

 sylvaticus. The division is founded chiefly on the fact, 

 that the front legs, though longer, are almost as thick 

 as the second pair, whilst in gamasus the front legs 

 are not only longer, but much thinner than the second 



Fig. I. — Ventral surface of Parasite of Water-Rat (magnified). 



pair. Murray ("Economic Entomology," Aptera), 

 objects to this genus on the ground that the figure in 

 Koch's Uebersicht does not bear out his diagnosis. 



Fig. 2.— Dorsal surface of Parasite of Water-Rat (magnified). 



This shows that Murray had not seen any of the 

 creatures, and probably had not seen the figures in 

 Koch's larger work. The specimens from which my 

 figures are drawn were sent to me for identification by 



