278 



this point seems desirable to see what liarmooy can be drawn from 

 the diÖerent observations. So far as possible when space permits, 

 the process is described in the words of the various con tributers to 

 this field. 



Between such outspoken descriptions as those of d'Haudiviller 

 for example, on the one hand, and Justesen, on the other, it is not 

 difficult to differentiate, but, in the cases where terms like sympodial 

 dichotomy and monopody with acropetal development of the lateral 

 buds are used, it is not always easy to determine whether the authors 

 have not been describing the same process with different words. At 

 the outset therefore it may be well to state that by monopody we 

 understand lateral outgrowths from the wall of the bronchus whether 

 they occur on the side of or above the terminal bud, and by dichotomy 

 we unterstand an undoubted division of the terminal bud. In equal 

 dichotomy the two divisions grow for a time equally but later may 

 give rise to a system of monopodial appearance by the selection of 

 one branch to continue as the stem, while in unequal dichotomy the 

 two buds develop unequally from the first. In the case of dicho- 

 tomous divisions, however, it is obvious the portion of the stem be- 

 tween two side branches is genetically equivalent to the side branch 

 of the lower order. 



Since one can explain theoretically the entire bronchial tree equally 

 well by either a monopodial or a dichotomous process of growth, it 

 is not surprising to find different views among those who have studied 

 only the finished bronchial system. This is well shown among the 

 modern investigators in the work of Aeby 1880 and Ewart 1889, the 

 former of whom believed in monopodial growth from first to last, 

 while the latter says: "Dichotomy is the alpha and omega of bronchial 

 division". Huntington 1898 also in working upon comparative material 

 of adult stages finds a double system primarily dichotomous with a 

 subsequent monopodial type of branching in the development of the 

 stem bronchus. In a system thus capable of two explanations, ob- 

 viously, the only observations which will really aid in solving the 

 question come from those who have studied the lungs during the 

 process of their growth. 



If we turn to this series of investigations we find Küttner 1876 

 stating that "Das Wachsen ist monopodisch, d. h. das Epithelrohr 

 wächst an seinem Scheitel ungetheilt fort, während seitliche Sprossen 

 am Stamm desselben hervortreten und mit ihrer Längsaxe zu der 

 des erzeugenden Rohres rechtwinkelig gestellt sind". Furthermore he 

 States that these buds grow and divide rapidly, giving rise to so many 



