Variation in the C:N ratio of substrate mineralized during forest humus decomposition

Laboratory incubations of sieved (<2mm) forest humus were used to study the response of C and N mineralization to perturbation. Considerable variation in the ratio of mineralized C to mineralized N was observed. This ratio widened with increasing temperature. At constant temperature, addition of P stimulated CO₂-C evolution and reduced NH₄⁺-N production, also widening the C:N ratio of substrate mineralized. Addition of weak base stimulated mineralization of N more than C, reducing the C:N ratio of substrate mineralized. Addition of weak acid, mineral-N, or excessive amounts of water inhibited CO₂-C evolution while stimulating production of NH₄⁺-N, resulting in a “negative correlation” between the two, and reducing the C:N ratio of substrate mineralized still further.Results were interpreted in terms of effects on microbial biomass. A relatively benign treatment (P addition) may promote microbial growth and respiration, reducing net N availability. A moderate perturbation (addition of weak base) favors new organisms growing partly at the expense of microbial necromass. These organisms will mineralize some necromass-N, increase net N mineralization, and reduce the C:N ratio of substrate mineralized. Under severe conditions (addition of acid) the C:N ratio of substrate mineralized approaches that of the microbial biomass itself, suggesting that the biomass is the primary substrate mineralized. Microbial mortality is likely to be a significant factor affecting the supply of N in field situations, and should be included in any general model of soil N mineralization processes.     

IMAGING DIAGNOSIS—USE OF RADIOGRAPHY,COMPUTED TOMOGRAPHY,AND ENDOSCOPY IN THE DIAGNOSIS OF ESOPHAGEAL PERFORATION BY AN EXTRA‐LUMINAL TRACHEAL RING PROSTHESIS IN A GOLDEN RETRIEVER

A 6‐year‐old neutered male, Golden retriever presented with regurgitation and excitement‐induced coughing. Two years prior, extra‐thoracic tracheal collapse was diagnosed and extra‐luminal tracheal ring prostheses were placed. Radiographs at presentation showed mineralized and undulant cervical tracheal cartilages. A dorsally broad‐based soft tissue opacity bulged into the caudal cervical tracheal lumen. Esophageal dysmotility and barium accumulation were identified at this level on contrast esophography. Computed tomography showed migration of a prosthetic tracheal ring, resulting in perforation of the esophagus. Hair, foreign material, and dynamic tracheal narrowing were identified on esophagoscopy and tracheoscopy, respectively. Esophagostomy and foreign body removal were performed.     

Clinical and pathological effects of the dermonecrotic toxin of Bordetella bronchiseptica and Pasteurella multocida in specific-pathogen-free piglets

The role of dermonecrotic toxin (DNT) of Bordetella bronchiseptica and Pasteurella multocida, purified by repeated chromatography in Sephacryl S-200 gel, in the pathogenesis of atrophic rhinitis (AR) of swine was studied bacteriologically, clinically and pathologically. Two-week-old specific pathogen-free (SPF) piglets were parenterally treated with 30 micrograms of DNT 3 times at 2-day interval and 7-week-old piglets were treated with 15 micrograms of DNT twice a week for 5 weeks. In 2- to 3-week-old piglets, both B. bronchiseptica DNT and P. multocida DNT produced nasal turbinate lesions with similar severity, characterized by damage of the cilia, epithelial metaplasia, intensive proliferation of osteoblasts, regressive changes, and diffuse osteocytic osteolysis. In 7- to 12-week-old piglets, treatment with B. bronchiseptica DNT failed to produce progressive changes in the nasal turbinates. Histopathological examination revealed osteogenic processes and osteoid synthesis besides the proliferation of osteoblasts and mild osteocytic osteolysis. Moreover, severe gross pathological lesions developed in the stomach, liver, kidneys, and lymphoid organs. The piglets' appetite and body weight gain gradually decreased during the DNT treatment and in the last week when the toxic signs appeared. Treatment of 7- to 12-week-old piglets with P. multocida DNT resulted in progressive AR. Histopathologically, diffuse osteocytic osteolysis was observed in the nasal turbinates. Neither clinical signs nor pathological lesions of the visceral organs developed in these piglets. The authors emphasize that the DNT of B. bronchiseptica basically differs from that of P. multocida in biological properties, though there are certain similarities between the DNTs.     

随机向量内在相关性的度量及指标聚类方法的改进

用两类所含指标全体所构成的向量的内在相关性度量来刻画两类间的距离,改进了一种指标聚类的方法.为此讨论随机向量的内在相关性度量、改进了的方法及该方法的并类距离单调性等问题.