18G4.] 



met ivith in t]ie Animal Economy . 



319 



mere trace of amyloid substance can be detected, and that only in tlie cells 

 of the bulb. If a number of embryo lambs, of various sizes, are placed 

 side by side, and a drop of a weak solution of iodine acidulated be allowed 

 to fall on a corresponding part of each, the peculiar brown stain produced 

 will be seen to increase in intensity up to a certain point. After the ap- 

 pearance of the hair, the stain gradually diminishes in intensity, showing the 

 lessening quantity of amyloid substance in the tissue. If the tails cut off 

 from a series of foetal lambs are placed in a vessel containing a very weak 

 solution of iodine acidulated, it illustrates (by the colouring) very strikingly 

 the increasing abundance of the amyloid substance in the epidermic tissue 

 up to a particular period (that is, when the hair is fully formed), and then 

 its gradual disappearance. The feet and hoofs similarly treated illustrate 

 the same for the horny tissue of this part. From the time that the foetus 

 of the sheep is nine inches in length (at which period the amyloid sub- 

 stance seems to be at its maximum), the amyloid substance contained in 

 the horny structure of the hoof gl'adually diminishes until shortly before 

 birth, when, even after prolonged boiling, scarcely a trace can be ex- 

 tracted from it. 



In the tissue of the lung of mammalian embryos, the amyloid substance 

 is at one period present in immense quantity. After the watery part is 

 driven off by evaporation, more than 50 per cent, of the dry residue is 

 found to be nothing else than animal dextrine. As the organ approaches 

 maturity, and the animal is about being born, but before it has yet drawn 

 a single breath, the amyloid substance is found to be reduced to a very 

 small quantity indeed, and in some instances to have absolutely disappeared. 

 The following Table shows the progress of this change in the lung of the 

 embryo of the sheep, and, I believe, very closely represents the correspond- 

 ing amount of change which takes place in the lung-tissue of other embryos 

 which I have examined, viz. of the rabbit, cat, dog, cow, rat, guinea-pig. 



Size and condition of the embryo. 



Amount of amyloid 

 substance contained in 



20 grains of the per- 

 fectly fresh lung-tissue. 



1st. 



2nd. 



3rd. 



4th. 



5th. 



Gth. 



Not quite 6 inches long, without any vestige of hair 



15 inches long ; covered with delicate hairs 



16^ inches long ; well covered with fine liair 



Nearly 20 inches long ; quite thickly covered with \ 

 wool, and evidently very near the time of birth J 



rO grain. 

 2*55 grains. 

 2-8 grains. 

 3*45 grains. 

 2 '2 grains. 

 A quantity too small 

 to be estimated. 



It would be no very easy matter to attempt to indicate precisely the con- 

 dition of development of the embryo at which the maximum amount of 

 amyloid substance is to be found in the tissue of vohmtary muscle ; in 

 embryos of apparently the same age and condition of development it is found 



