522 



SCIENCE. 



[N. S. Vol. VII. No. 172. 



8. For reasons detailed, the primitive 

 type of the mammalian lung is the sym- 

 metrical ' bilateral hyparterial ' form, the 

 symmetrical ' bilateral eparterial ' form 

 representing the end-stage in the process of 

 evolution, not the primary type (Aeby, 

 Wiedersheim) . 



9. The primitive type of division is prac- 

 tically dichotomous {Hystrix, Taxidea) . 



We can recognize two main trunks on 

 each side, one cephalic, the other caudal. 

 The cephalic trunk supplies the anterior 

 and middle portions of the lung, the main 

 migratory modifications in the different 

 types taking place within its region of dis- 

 tribution. The caudal branch supplies the 

 posterior and larger portion of the lung. 



In the subsequent development of the 

 stem-bronchus and its monopodic type of 

 branching, characteristic of the majority of 

 mammalian lungs, the following factors are 

 active : 



a. Complete segmentation of the primi- 

 tive tracheal bulla, producing the usual 

 bifurcation. This establishes the proximal 

 portion of the stem-brouchus, and gives to 

 the primary cephalic trunk the position of 

 a lateral branch derived from the same. 



b. The caudal continuation of the stem- 

 bronchus is composed of the representative 

 elements of the primary caudal trunk and 

 its medial secondary branch, the lateral 

 secondary branch and additional lateral ac- 

 cessory branches developed subsequently 

 appearing as the ' ventral branches of the 

 stem-bronchus' (Aeby). 



c. The cardiac bronchus usually appears 

 as a special accessory branch derived from 

 the stem-bronchus of the right side only 

 (Exception Auclienia') . 



10. In the majority of forms examined, 

 the pulmonary artery is not dorsal to the 

 stem-bronchus, except in the terminal por- 

 tion. The position, as N"arath has pointed 

 out, is lateral or dorso-lateral. 



11. Hence the distinction into ' dorsal ' 



and ' ventral ' branches, separated by the 

 pulmonary artery in Aebj'^'s sense, should 

 be abandoned. 



12. The results above outlined agree with 

 the conclusions reached by ISTarath in re- 

 gard to the equivalence of the anterior or 

 cephalic branches of right and left side in 

 asymmetrical lungs. They differ in the in- 

 terpretation of the derivation of the ' Apical 

 bronchus,' which he regards as the dorsal 

 branch of the first ventral bronchus, and in 

 the above outlined phylogenetic develop- 

 ment of the stem-bronchus and its mono- 

 podic system of branching. 



The conclusion of the paper deals with 

 the probable causes which lead to the mi- 

 gratory changes in the relative position of 

 the cephalic branches. 



G. S. Huntington. 



Columbia University. 



SINGULAR STRESS-STRAIN RELATIONS OF 

 RUBBER. 



Since the stress-strain diagrams from rub- 

 ber were published in this Journal of date 

 of February 19th, last, the investigation 

 has been somewhat extended. In all cases 

 the same curious behavior was noted and 

 the same peculiar differences compared 

 with other materials. In all cases the sub- 

 stance behaved under load precisely as do 

 other materials in the eai'ly part of its 

 strain ; then a reversed curve is described 

 and the test-piece stiffens greatly and offers 

 continually increasing resistance until, at 

 last, rupture takes place, without yield- 

 ing by inelastic deformation at any point 

 in its course. Toward the end of its test 

 the substance yields pi'oportionately to the 

 applied load. The fracture is sharp and 

 without warning and the break clean and 

 smooth and at right angles to the line of 

 pull. No permanent reduction of section 

 is observable after fracture. The reduced 

 section immediately before breaking was 



