4: CHARLES F. W. MC CLURE 



environment, a balance is soon established between the amount 

 of water driven through the integument into the subcutaneous 

 lymph sinuses and that excreted by the kidneys (Overton, 

 '04), so that the relatively large amount of free water con- 

 tinuously added to the lymph does not accumulate in the body 

 in excess. A normal frog 1 transferred from water at one 

 temperature to water at another ordinarily either loses in 

 weight or remains stationary; and in the cases where it 

 gains weight, the gain is never so continuous through an 

 extended period of time as to produce an oedema. It is there- 

 fore evident that when lymph continues to accumulate in 

 the body in excess of normal, the gradual and continuous 

 increase in body weight must be attributed to some factor or 

 factors other than normal, which inhibit the establishment 

 of the balance normally existing in the body between the flow 

 of incoming and outgoing water. Whatever it may be in 

 other animals, the explanation of oedema in the frog depends 

 on the determination of such factor or factors. 



In its passage through the capillary vessels of the blood- 

 vascular system, some of the plasma escapes, or transudates, 

 through the capillary walls into the tissue spaces, where it is 

 either taken up by the tissues or returned to the lymphatics. 

 The transudate constitutes what is ordinarily regarded as 

 the lymph concerned in oedema; and all existing theories of 

 oedema attempt to explain the process by which this lymph 

 accumulates and is retained in excess of normal in the tissues 

 and cavities of the body. An oedema of this character may 

 be spoken of as an intracellular (interstitial V) oedema, since, 

 owing to the presence of the lymph in excess of normal in 

 the tissue cells, tissue spaces, and cavities of the body, the 

 oedema is evidenced chiefly by a swelling of the tissues in 

 which the lymph has accumulated. Under certain patho- 

 logical conditions, this form of oedema occurs in the frog, 



1 Unless otherwise stated, Etana pipiens (Screber) is the species of frog used in 

 all the experiments of this investigation. 



2 It may be regarded as largely an academic question whether the oedema is 

 purely intracellular or interstitial in character; while without doubt it is largely 

 interstitial, it must to some extent also be intracellular. 



