1890.] of the stem in the Cucurbitacece. 67 



live. We have seen that in the herbaceous species a large amount 

 of xylem is not needed ; but, by comparison with other herbaceous 

 plants, we see that a considerable amount of phloem is necessary. 

 This phloem receives considerable additions before the bundles are 

 closed, and we may infer that it is more beneficial that the phloem 

 should be divided by the xylem than that it should be placed only 

 on the exterior of the xylem. 



In the woody perennial species, the amount of internal phloem 

 is not large ; and the requisite amount is formed in the normal 

 way by the cambium as growth in thickness takes place. These 

 stems have no sclerenchymatous ring, and hence derive their 

 support from the xylem and external objects, and hence, as the 

 tree grows larger, continual additions are made to the vascular 

 bundles. 



[Received March 9, 1890.] 



(3) Note on the action of Rennin and Fibrin-ferment. By 

 A. S. Lea, Sc.D., Caius College, and W. L. Dickinson, Caius 

 College. 



[Reprinted from the Cambridge University Reporter, March 18, 1890.] 



The experiments which were demonstrated to the Society 

 were made in order to verify some recent statements of Fick 

 {Pflugers Arch., Bd. 45, 1889, S. 293). This observer had urged 

 that rennin certainly, and fibrin-ferment probably, produced their 

 respective actions on milk and blood-plasma without the necessary 

 contact, throughout the whole fluid mass, of the ferment molecules 

 with the molecules of casein and fibrinogen. If this were so, then 

 the mode of action of these ferments would be strikingly different 

 from that of the ordinary digestive ferments. Fick based his 

 views upon the result of an experiment made by placing a 

 glycerine extract of rennin at the bottom of a tube, carefully 

 pouring some milk on the top of the glycerine and observing that, 

 without mixing the two fluids, the milk rapidly clotted throughout 

 its entire mass. 



The authors experimented by warming milk to 40° C. in a 

 test-tube, and then carefully introducing, by means of a fine glass 

 tube, an active extract of rennin below the milk. The constant 

 result of this experiment was that a clot was rapidly formed at 

 the junction of the two fluids, but that not until the lapse of 

 several hours was the milk clotted throughout. When a similar 

 experiment was made with dilute salt-plasma a narrow clot of 

 fibrin was similarly formed at the junction of the plasma and 

 fibrin- ferment solution. But unlike the case with milk, the super- 



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