578 LECTURE XXIV. 



of the transudates the question has been much discussed whether they 

 result from a filtration from the blood-vessels or whether they represent an 

 " active" secretion. Here the relations are somewhat similar to those of the 

 lymph. The fact that transudates contain the same substances as plasma, 

 and, with the exception of albumin, in about the same proportion, cannot be 

 regarded as an absolute proof of a filtration having taken place. Under 

 pathological conditions the amount of transudate may increase enormously. 

 If this formation results from an inflammatory process, it is called an 

 exudate. The exudates are richer in cellular elements. If the amount 

 of the latter is greatly increased, we called the liquid pus. 



Transudates are found normally in the sac of the pericardium, between 

 the layers of the pleurae, and in the peritoneum. To this class of liquid 

 belongs the cerebro-spinal fluid and perhaps also the aqueous humor. A 

 very similar liquid is found around the joints and in the bursce mucosce 

 which is known as synovia. It contains a substance similar to mucin. 

 The true transudates are composed, as we have said, of the same con- 

 stituents as plasma, and it is noteworthy that they contain fibrinogen, 

 but hardly to an extent sufficient to permit spontaneous coagulation. 



If we examine more closely the relation between the lymph and the 

 blood, we shall arrive at the conclusion that, to a certain extent, all the 

 cell-elements of the animal tissues are either directly or indirectly mois- 

 tened by these fluids. The tissues no longer appear to us as rigid struc- 

 tures, as it is customary to consider them from an anatomical point of 

 view. There are no sharp lines drawn between the blood, lymph, and 

 the body-cells. There is never any repose. A stream of blood continu- 

 ally flows towards the cells, and conversely, the cells by the aid of the 

 lymph send their products to the blood, and thus all the different ele- 

 ments combine to form a physiological unit for each individual organ, or 

 perhaps only for definite cell-groups. We can now understand what 

 great difficulties are met with in the attempt to trace experimentally the 

 course of a reaction in the animal organism. The lymph forms on the 

 one hand an intimate mean's of communication between the blood and 

 the tissue-cells, and on the other hand it serves as a barrier between 

 them. Substances administered, whose participation in cell-metabolism 

 we should like to be able to trace, may reach only as far as the lymph, and 

 may be excluded from the metabolic processes of the cell itself. Whether 

 transformations take place in the lymph, or whether the lymph modifies 

 the products obtained from the blood and prepares them so as to meet 

 the existing demands, is something of which we have no information. 

 Here a great unexplored field lies before us. 



