246 EXTRACTS AND ABSTRACTS FROM FOREIGN JOURNALS. 



M. Tristrans third Memoir on Phytology . This memoir is confined 

 to the study of the spiral and large sap vessels. 



The author considers that certain spiral vessels have originally been 

 formed of a simple membrane, which is afterwards cut down into a 

 helix ; but he maintains that other spiral vessels, or tracheae, are origin- 

 ally formed by one or more filaments which grow at their extremity, 

 turning in a helix, and to these there may afterwards be added a mem- 

 brane, which unites the turns of the spiral. He considers that the 

 position of the tracheae is too much restricted, when they are supposed 

 to be confined only to the medullary sheath. He believes that plants 

 (cifaisceaux didynamesj should be considered as having their tracheae in 

 the thickness of the ligneous substance. In other plants he shows the 

 elements of the tracheae (under the name of scattered filaments) even in 

 the external ligneous layers of the stems of several years growth. 



With respect to the sap vessels, he endeavours to recognize the more 

 essential features of their different forms, with a view to their classifica- 

 tion, according to a natural method; but there is so much obscurity 

 still on this subject, that the author conceives that it is necessary to 

 adhere at present, at least provisionally, to an artificial method, which 

 he proposes. 



M. Arago presented to the academy a microscope, manufactured by 

 Lerebours, and furnished with achromatic lenses of very short focal 

 distance, executed by M. Nachet. One of these lenses was ground in 

 a curve, the radius of which was half a millimetre. 



M. Gruby (( On the Entozoa of the Frog, and on some Points in the 

 Pathology of that Batrachian." . M. G. remarks that 



" The existence of several species of entozoa in different parts of the 

 bodies of frogs, is known to every one ; he himself has observed them 

 frequently in the urinary bladder, in the cellular tissue which surrounds 

 the subclavian veins ; in the lungs ; in the intestines, and in the cellular 

 tissue of the peritoneum. In the latter situation the worms were 

 enclosed in small pouches of i to ^ of a millim. The pouches being 

 transparent, enabled M. Gruby to see the entozoa within them mani- 

 festing every sign of vitality : these were of the genus Filaria, and their 

 different parts could be readily distinguished. He saw the ova of this 

 entozoon not only circulating in the vessels with the blood, but saw 

 them also in the spinal canal. He observed some Ascarides within the 

 sheath of the nerves, among the primitive nervous fibrillae. The length 

 of these worms was from -^ to -^ millim.; their width ^^ millim. : 

 they were transparent, and moved slowly. 



In the lungs, they were lodged in the air cells, surrounded with a 

 yellowish, firm substance, presenting under the microscope, all the 

 characters of tuberculous matter. 



Desirous of studying the cause of the formation of these tubercles in 

 the lungs of the frog, he injected ovula into the blood of this animal, 

 and observed that some were arrested in the capillary net work of the 

 lungs, and some in that of other transparent portions of the body. He 



