58 CONNECTIVE TISSUES. 



tended more and more, until it forms around the globule a 

 thin investment, in which lies the clear oblong nucleus. In 

 well-developed fat cells, which usually lie together in groups, 

 it is not possible to observe processes. They rather resemble 

 closely packed globular structures. 



Transition Forms bet-ween Connective Tissue 

 Corpuscles and Fat Cells. If, in a rabbit, the skin and 

 subcutaneous tissue are divided over the inner (anterior) third 

 of the infra-orbital edge, and the thin membrane which stretches 

 over the infra-orbital fossa is severed, it is easy to remove, 

 along with the glandula infraorbitalis, a gelatinous hj-aline 

 mass. If, from this mass, a very thin portion is snipped off 

 and placed in a drop of fresh serum on a glass slide and 

 covered, it is easy to distinguish, among the ordinary branched 

 cells, others which are larger and contain globules of fat. All 

 transitions ma}'' be seen between those which contain one or 

 two small droplets and those which are completely distended. 

 These structures will be referred to again, under another 

 heading. Fat cells are, as a rule, collected in masses around 

 bloodvessels. 



v Tendon Cells. The cells of mature tendon tissue do not 

 /essentially differ from those of ordinary connective tissue. 

 Like them, they are oblate branched masses of protoplasm, 

 which are in communication with one another by their pro- 

 cesses. They are not, however, flat, but curve themselves in 

 conformity with the surfaces of the individual bundles to 

 which they are applied. In order to study them, the best 

 material is afforded by the tail-tendons both of young and full- 

 grown rats or of rabbits, which can be examined either in the 

 fresh state in serum, or by steeping them for a few minutes in 

 silver solution, after they have been first pencilled with a 

 camel-hair brush dipped in fresh serum. Another material 

 which may be used is the centrum tendineum of the diaphragm. 

 In very young animals the caudal tendons present a peculiar 

 arrangement. If the tail of a very 3 r oung rat is amputated, 

 and the tip torn asunder from the cut end, a great number of 

 isolated lengths of tendon are obtained, of almost microscopic 

 tenuity. These may be at once separated, and covered in very 

 dilute acetic acid. Such a preparation shows, between the in- 

 dividual bundles, chains of apparently quadrangular masses 

 of protoplasm, each containing a roundish nucleus. These 

 chains alternate in position with the bundles. If, however, a 

 single cylindrical bundle of fibrils is separated, it is seen that 

 it possesses an envelope of granulous protoplasm, which ex- 

 tends along one side of the bundle, covering nearly half of its 

 circumference ; in this envelope nuclei lie arranged in linear 

 series. If the preparations are treated with stronger acetic 

 acid, the protoplasm between the nuclei exhibits cross lines of 



