G. GENERAL NATURAL HISTORY AND ZOOLOGY. 347 



may afford a physiological explanation of the phenomena in 

 question by affecting certain portions of the brain, and the 

 involving of other portions by sympathy. 



The following experiments serve to illustrate the charac- 

 teristic effect of constrained attention. If a thread be sus- 

 pended over the comb of a chicken so that the ends hang 

 down over the eyes, the fowl will remain in a perfectly cata- 

 leptic condition, and finally pass into somnolence, so deep, in- 

 deed, that it will permit all possible movements, as turning 

 the head up and down, etc., without giving any signs of life. 

 Again, if a j^igeon be pressed gently npon a table, so that it 

 can not use its wings, and a finger be placed before its eyes, 

 and moved back and forth, following the motion of the head 

 so that the eyes must continually notice it, the bird will soon 

 become quiet, and will not fly away when the hand is re- 

 moved. Similar consequences result in case of many human 

 beings. If the eyes be directed fixedly to one point for some 

 time, they fall into a sleep which may be regarded as the 

 simplest manifestation of mesmerism. 1 C, ix., 49. 



REGULATING THE GROWTH OF BOXE IX YOUNG ANIMALS. 



M. Oilier announces, as the result of recent experiments, 

 that he has succeeded in very considerably modifying the 

 growth of bone, by local irritation during the period of de- 

 velopment, lengthening it or arresting its growth, according 

 as one part or the other of the bone is dealt with. Thus, an 

 irritation upon the central part of the long bones, if of suffi- 

 cient amount and long continued, causes elongation ; but 

 when this affects the periosteum, the marrow, and the bony 

 substance properly so called, it produces hypertrophical phe- 

 nomena. The methods of producing this irritation, and the 

 consequent growth of the bone, are very varied. Incisions, 

 excisions, cauterizations of the periosteum, irritation of the 

 marrow by perforation, and the implantation of foreign bod- 

 ies are followed in young animals by an elongation of the 

 bone. It is by no means necessary to produce suppuration 

 in order to accomplish this result, a subacute but prolonged 

 irritation beins: more efficient and less danorerous. The in- 

 crease thus secured is in proportion to the persistence of the 

 experiment, and may amount to one tenth of the total length 

 of the bone. This elongation is produced, not by interstitial 



