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Dr. McDonnell 07i the Amyloid Buhstance [June 16, 



several of them of amyloid substance in abundance ; but neither of these 

 observers has attempted to show, by chemical investigation, at what 

 period of development each of the tissues containing it is found to have it 

 entering most largely into its composition. It must be remembered that 

 the acidulated tincture of iodine is a test of such delicacy for this substance, 

 that it produces its characteristic reaction even when the quantity of amy- 

 loid substance present is very minute hence, judging from the use of this 

 test under the microscope, one is apt to suppose that the amount present is 

 greater than it really is, or rather that it is equally abundant in tissues 

 which in reality contain it in widely different quantities. 



It was possibly owing to this mode of examination that Professor Bernard 

 was led to suppose that this substance continues to exist in muscular tissue 

 during the entire period of intra-uterine life, and that it does not disappear 

 until after birth, when it does so under the influence of the respiratory 

 and muscular movements. I hope to be able to show, however, that the 

 establishment of respiration has little do with the disappearance of the 

 amyloid substance from the tissues of the foetus, and to prove that, in 

 truth, certain azotized tissues are evolved from a nidus of amylaceous pro- 

 toplasm, which, after a particular stage of growth, becomes less and less 

 as each of those tissues approaches maturity, and that when maturity is 

 attained the amyloid substance, which once formed so large an ingredient 

 of the growing tissue, has gradually become changed so as to be no longer 

 discoverable, even before respiration has commenced. 



M. Rouget has quite correctly pointed out the very early period at which 

 the amyloid substance is found in the cartilaginous tissue : it first shows 

 itself in the cellules of this tissue ; in the embryo chick and lamb, at a 

 very early stage of development, it may be demonstrated ; it very soon, 

 however, disappears from the cells of cartilage and is too small in amount 

 to be estimated at different stages of growth. 



The epithelial cells of the skin are rich in amyloid substance at an early 

 period. The points where cells aggregate themselves together for the com- 

 mencing development of a feather or a hair, show a great abundance of the 

 amylaceous material. The horny appendages of the skin, the bill of the 

 embryo chick, the claws, hoofs, &c. of other embryos, contain it in large 

 quantities up to a particular period of development. The feet of a fcetal 

 calf of about four months were dried at a heat not exceeding 212° ; 7 grains 

 of the horny structure were rasped off, and on examination yielded 1*3 gr, 

 of amyloid substance. An exactly equal quantity from the feet of a nearly 

 full-grown foetal calf, similarly treated, gave an amount of amyloid sub- 

 stance too minute to be estimated. It almost wholly disappears from the 

 feathers when they become prominent on the surface, and for hairs the 

 same may be said. If one of the large hairs from the eyebrow of a fcetal 

 lamb, shortly before the time of birth, be examined, nothing more than a 

 * A tenth of a grain of amyloid substance may be readily detected in an ounce of 

 water by the action of acidulated tincture of iodine. 



